Legionella pneumophila, the causative agent of Legionnaires' Disease, is a gram-negative bacterium that evades delivery to the lysosomes of alveolar macrophages by arresting phagosome maturation. We can use this intracellular pathogen as a tool to study critical functions of macrophages, such as endosomal/lysosomal trafficking. L. pneumophila can facilitate inhibition of phagosome maturation by modifications of its surface properties expressed during the post-exponential (PE) phase of growth. Analogous to the developmentally regulated lipophosphoglycan of Leishmania spp. which blocks phagosome maturation, we hypothesize that L. pneumophila expresses a regulated surface glycoconjugate, likely lipopolysaccharide (LPS). Our objective is to identify the glycoconjugates that are modified during the transition to L. pneumophila's virulent phase and their specific roles in phagosome maturation. Specific aim 1 is to screen an established mutant library for their crystal violet binding properties and isolate those mutants which abnormally bind crystal violet in the PE phase, thus indicating abnormal surface properties. Specific aim 2 is to construct mutants of the genes encoding LPS biosynthetic genes to determine if these genes are required to block phagosome maturation.